I know by experience that rostratas hate to have their roots disturbed. Rot is easily distinguish by pressing the stem near the soil base. If healthy it should feel solid and woody, NOT spongy. It looks to me that Tom's Yucca is lacking water. The trick with succulents is to let them dry between watering. The more water the more growth.

I sold the house to my brother and he wanted it. I told him if he ever gets tired of it to send it my way.

Check with Joe at Triple Oaks Nursery in Franklin. It may be a little off the beaten path for you in south central NJ., but he has a great selection of all sorts of palms, camellias, and overall unique not run of the mill things. I don't remember seeing trunking yuccas for sale but I could be wrong. He has his own message board so you can post and ask him. Regardless, it's worth a trip just because of the great selection. I've seen taller rostratas and other trunking yuccas in that area so they are getting them from somewhere. If anybody would know, Joe or Jim Kelly would know. Jim is a regular poster on the NE palm board. Great guy even though he roots for crappy teams that never win anything significant (hope he sees this). Also as far as yucca boards go, the Yucca Yucca board is the only one of significance although it has been dead lately. But all of the yucca 'big boys' are on that board. http://members6.boardhost.com/yuccayucca/

I bought one called 'Sapphire Skies' three weeks ago, a 3 gallon Monrovia Plant. It is listed as hardy to zone 5. You are not being excessive in your 3ft hole filled with rock and sand. But I would suggest leaving some dirt, mixing in coarse sand with it and building it up into a well draining mound. If its really awful clay, get rid of it but if its decent soil, use it to build up the height. The drainage is often more important than the temperatures. That is how I planted mine. I got some bags of topsoil and a LOT of sand and its mounded up pretty high. Sort of adds to the look of it planted as well being raised up like that. I agree with nmgirl. Sounds like a sunburn. If so, those burns will scar the leaves permanently. I always bring my non winter hardy cactus type plants out as early as possible and set them in a protected spot with shade that gradually becomes sunny as the sun moves higher. That way they get the spring rains and harden up real nicely. These are tough hardy plants that thrive on neglect and they don't like being babied. Kindness is often a killer.